Radar signal simulator



March 8, 1960 J. w. RUBINO ETAL RADAR SIGNAL smuLA'roR 2 shets-sheet 1 Filed Feb. 15, 1954 ATTORNEY March 8, 1960 J. wQRUBlNo ETAL RADAR SIGNAL srMuLAToR 2 Sheets-Sheet 2 Filed Feb. 15, 1954 G G. N w my m ma wm mmv Mw u w. A6 m0 Anw .A P p am J A mm M N mw. mw ww mw. am o a RV Rw Mw sp Il. I 40M, A .f u A I lll f W l l IM# am Q l w l V Lum l A C D v... F C H I J WU NNQO III' v L,

n A O A Y. rw. MWL m a ef o MUN T 0 1 VRM T o E W00, WMI .A o w H A P M a n o... N EJL a n n l. Y c n B Ff, a, c A Mm AlwvSSglv L d .le Im w.. lr a I M k L M Tmwfkqgl# RADAR SIGNAL SIMULATOR John W. Rubino, FortILee, and Leon Himmel,. Cedar Grove, NJ., assignors to International Telephone and Telegraph Corporation, Nutley, NJ., a corporation of Maryland l Application February 15,` 1954, Serial No. 410,365

V8 Claims. (Cl. 34E-47.7)A

Thisz invention relatesY to` modulated pulse generators` and more particularly to test equipment which is' capable' of simulating the characteristics ofA many'types of received radar signals.

It is well-known that in recent years much engineering effort has been directed to the design and development of receivers capable of detecting' radar signals. Such re'- 'ceivers are extremely usefuly as counter-measure devices;

that is devices capable of` giving' warning when the radiations of radar transmitters are detected. Although great expenditures of time and money have been put into the development of radar warning receivers little effort Was directed to the testing of such equipment; There has been felt a great need for a signal source whoseoutpnt simuantenna' rotation and beam Width or it must provide" means to simulate a radar which is tracked on to a targetand thus required no amplitude modulation or simulated'antenna rotation. The pulse source ofthe desired' test equipment besidesl having a repetition rate which is controllable must have a pulse width which is variable andthe output of the test equipment mustbe of proper magnitude and sign to cooperate'with other test equipment. f -V One ofthe objects of this invention, therefore, is to provide a source Vof simulated radar signalsv whose output signalV characteristics can be varied to duplicate ther rc-v ceived signal due to anyone of many types of radar systems; t

Another object'of this invention is to provide an'amplitude modulated pulse generator test equipment in whichv the repetition rate of the amplitude modulation signal and the pulse repetition rate,V aswell as the pulse width and the modulation signal width, can be varied within a wide limit.

A further object of this invention is to provide a testpulse generator whose output provides modulated pulses simulating the envelope waveform of the detected signal transmitted by a typical rotating beam radar system and the test generators having" provision for adjustment of both beam width and simulated radar rotational rate as well as being capable of an unmodiulatcd pulse output modulation generator can be controlled widthor rate,

In order to be most useful such asignal source States Patent ice simulating; avariation in a transmitted radar signallheam,

width or the rotational rate of a transmitting antenna.

. various` portions of the block-diagram shownin Fig. 1. Eig; 3v is a graphic illustration ofi aseries of curvesnot is attenuatedto provide an` output level consistent with predetermined needs. l

The above-mentioned` andother features and objectsofthis invention will become more'apparent by referencczto.

the following description taken in conjunction; with. the:

accompanying drawings, in which;

Fig..1 is a schematiofdiagram in blockforu'tofi one embodiment of a radar-signal simulator in accordance.

witnthe principles of this invention; and:

' Eig. 2 is a graphic illustration of a series of; curves plot.-

ting4 voltage `versus time. showing waveforms present inY plotting voltage versus time showing waveforms present in various portions of theblockdiagram shown in Fig. l

but havingralarger time scale than the waveforms' of'- YFigl v4 is a graphic illustration; of a series-.of curves ploty ting voltage versus time showing waveforms present in various portions, of the block diagramshownin Fig. `1` but having alarger time scale than the waveform.; ofY

Fig.

Referring to Fig. l', a schematic diagram in block form of one` embodiment ofthe radar signal simulator ot this invention is. shown wherein the, waveforms illustrated in,

Figs. 2`4 present in various points of the block diagram f of Fig. 1; are indicated by corresponding letters to indicate: the points Where the waveforms of Figs.v 2-4 are found. A modulation generator i generates a modulat ing waveform which isv coupled to a modulatory 23 by means of a switch i7 to modulate a pulse outputfrorn a pulse generator 2. The modulated pulse output is coupled to. a distribution circuit 3, making available at the output taps of the distribution circuit signals whichVVV closely simulateV energy detected by aV receiver located in the energy transmission path of the antenna of a radar system. Referring to the modulation generator 1, a sine wave-oscillator 4generates a sinusoidal output AiA which is appliedto a half wave rectiiier 5 and a squaring circuit 6.- The frequency of the output of sine wave oscillator 4 may be varied within wide limits. The energy coupled to the squaring circuit 6 is converted into a squarel wavef- Y form shown in curve B and coupled to a dilerentiator circuit 7 whose output shown in curvo D comprises a series of positive pulses 7a coincident in time with the,

leading edge ofthe square wave of curve B and a sexies of negative pulses 7b coincident in time with the trailing edge ofthe square wave of curve B. The negative pulsed output 7b of dierentiator circuit 7 is transformed into a series of positive pulsesshown in curve E through the use of the inverter circuit S whose output waveform E isocoupled to a modulator gate generator 9. The positive pulsed 1 output 7a of differentiator circuit 7 is c oupled'to an amplitude sensitive gate it) whose output shown in curve F is responsiveV to the output H of the adjustable bootstrap timing generator i3. The output of amplitude sensitive gate 10 is coupled to the modulator gate generator 9. Each time a negative pulse 10a is coupled from the amplitude sensitive gate 10 to the modulator gate generator 9, it turns on generator 9 causing a gating voltage shown in curve G, to be coupled to a revolution per minute (rpm.) gate 11. Thev gating voltage output G from the modulator gate generator 9 is shutrolf when the positive Patented Mar. s, 1960 pulse of curve E is coupled from the inverter 8 to the modulator gate generator 9. Thus, it is apparent that the gating voltage shown in curve G coupled to the r.p.m.v gate 11 from the modulator gate generator 9 comprises substantially a square wave having its leading edge 11a coincident in time with the negative on pulse 10a, curve F, from the amplitude sensitive gate 10, and its trailing edge 11b coincident in time with the next positive off pulse, curve E from inverter 8.

The output G of the modulator gate generator 9 closes electronic switch 12 sending a signal to the bootstrap timing generator 13. The waveform shown in curve H is generated by the bootstrap timing generator 13. When a certain voltage level of curve H is reached the output' of the modulator gate generator may also be coupled toy ditferentiator 14 whose output comprises a plurality of synchronous pulses shown in curve J in synchronism with the r.p.m. gating voltage G. The output] of differentiator 14 is coupled to a phase splitter 15 to provide output pulses of a positive or negative polarity in synchronism with the'modulation waveform. The r.p.m. gate 11, controlled by the output G of the modulator gate generator 9, opens to permit a portion of the output C of a half Wave rectifier 5 to be passed to an inverter 16 whose output I comprises the modulation waveform -which is coupled to the input switch 17 of the pulse ,generator 2.

Switch 17 allows the output of pulse generator 2 to be eithervmodulated or unmodulated depending upon the position of the switch armature 17a. For purposes of explanation, assume that it is desired to have an amplitude modulated pulse output from the pulse generator 2. A pulse oscillator 18 is provided whose pulse repetition frequency may be varied within wide limits to a desired The output shown in curve K, of oscillator 18 is coupled to a squaring circuit 19 whose output shown in curve L is shaped in pulse Shaper circuit 20. The output waveform M of shaper circuit 20 is coupled to the input of multivibrator 21 whose output comprises a series of pulses similar to the input pulses M but having a width or duration that can be varied. The output of the pulse width multivibrator 21 is inverted in circuit 22 whose output N is coupled to modulator 23 along with the modula-4 tion waveform for modulation generator 1. The pulsev The modulated pulse output of pulse generator 2 is coupled to a plurality of phase splitters 25 in the pulse distribution circuit 3. The output of the phase splitters 25 can be etherpositiv'e or vnegative as selected by switches 26. The output of the switches '26 are coupled to anattenuator 27 in'each of the outputchannels, thus individual control of the output amplitude is aorded.

Referring to Fig. 2, it is seen that the output waveform shown in curve Q has a sbape substantially equal to the shape of an envelope wave detected by a receiver that is in the field of transmission of a rotating antenna of a radar system. Obviously, if the simulated radar system has a greater or lesser rotational rate for its antenna the modulated pulse output of curve Q can increase or decrease its repetition rate by merely increasing or decreasing the timing of the adjustable bootstrap timing generator 13 which, in turn, would control the increase or decrease in the opening and closing of the r.p.m. gate. Since the control signal for the r.p.m. gate 11 is responsiveto signal derived from the sine Wave oscillator 4, it is obvious that the beam width of the output of oscillator 4 will be coordinated with the repetition rate due to the opening of gate v1.1 and the greater the repetition rate the lessv the beam width due to the output of oscillator 4.

It-is also obvious that if theradar Ysystem to besimu-` lated hasan increased pulse repetition rate this canbe ing the pulse repetition frequency of oscillator 18. To simulate a variation in the duration or width of the pulses emitted by the radar systemto be simulated, it is only necessary to adjust the multivibrator 21 whose output pulses N can have a greater or lesser duration. Some radar systems after searching out a target will lock on and continue to track the target. The signals detected by a receiver located at a tracked on target will not be amplitude modulated because the antenna is no longer rotating but is focused upon the detected object. To simulate such a locked ou radar transmitter it is necessary to eliminate the amplitude modulation of the pulse output of generator 2. This is accomplished in the equipment of this invention by moving the armature 17a of switch 17 from the on position to the off position. The reception of radar signals decreases in amplitude proportional to the distance between the receiver and the transmitter.

To simulate transmitters at varying distances attenuators 27 are-provided in distribution circuit 3. The greater the attenuation introduced by circuits 27, the greater the simulated distance between the radar system and receiverv under test.

While we have described above the principles of our invention in connection with specific apparatus, it is to be clearly understood that this description is made only by Way of example and not as a limitation to the scope of our invention as set forth in the objects thereof and in the accompanying claims.

We claim:

l. A vmodulation signal generator comprising a source of sine wave signals, means to vary the frequency of said sine wave signals, means to rectify said sine wave signals,

' means to generate a control signal responsive to said sine wave signals, means to vary the repetition rate of said control signal, and gating means responsive to said control signal and coupled to the output of said rectifiermeansto pass certain of said rectified sine wave signals. I '2. A modulation signal generatorv according to claim 1 which further includes means responsive to said control signal coupled to said means to generate said control signal to generate a synchronizing pulse each time said gating means passes one of said rectified signals.

3. A radar signal simulator to produce a modulation signal havinga waveform substantially equal to the shape of the envelope wave detected at a receiver due to thel transmission radiated by a rotating antenna of a radar transmitter comprising a modulation generator to produce the envelope characteristic of a signal radiated by a rotating radar antenna, said modulation generator including a source of sine wave signals, means to vary the frequency of said sine wave signals, means to rectify said sine wave signals, means to generate a control signal responsive to said sine wave signals, gating means responsive to said control signal and coupled to the output of said rectifying means to'pass certain of said rectified sine Wave signals as the output of said modulation generator, pulsel generator means to generate a plurality of pulses, and modulation means to amplitude modulate said pulses with said output of said modulation generator.

4. A radar signal simulator according to claim 3 having further means'to vary the repetition rate of said control signal.

5. A radar signal simulator to produce a modulation signal having a waveform substantially equal to the shape of the envelope wave detected at a receiver due to the transmission radiated by'a rotating antenna of a radar transmitter comprising a modulation generator to produce the envelope characteristic of a signal radiated by a rotating radar antenna, said modulation generator including a source of sine wave signals, means to vary the frequency' of said sine wave signals, means to rectify sagdrsine wave signals, means to generate a control signal responsive to said sine wave signals, gating means responsive to s aid control signal and coupled to the output ofsaid rectifying means to pass certain of said rectified sine wave signals as the output of said modulation gen erator, pulse generator means to generate a plurality of pulses mcluding-means to vary the frequency of said pulse generator and means to vary the Width of pulses from fsaid pulse generator, and modulation means to amplitude modulate said pulses with said output of said modulation generator. t

6. Avmodulationisignal generator comprising a source 1 Vof sine wave signals, means to rectifyv said sine wave signals coupled to said source, means to generate a con- 1 trol s1gnal responsive to said sine wave signals including a squarer coupled to the output of said source, atrst lditerentiator,` means couplingsaid first diferentiator `to said squarer, a first inverter, an amplitude sensitive gate, means coupling the negative output of said iirst differ- -entiator to said first inverter, means coupling the positive output of said dilerenti-ator to said amplitude sensitive gate, a modulator gate generator, means coupling the outputs of said first inverterand said amplitude sensitive gate to said modulator gate generator, a boot strap timing generator, Van electronic switch coupling the output of said modulator gate generator to said boot-strap timing generator, means'coupling the output of said boot strap timing generator to said amplitude sensitive gate; a revolution per minute gate coupled to the output of said rectifying means, means coupling the output of said modulator gate generator to said revolution per minute gate to pass certain of said rectified sine wave signals 're, Vsponsive to the output of said modulatoi gate generator,

a second inverter, means coupling the voutput of said revolutiongper minute gate to said second inverter to obtain as the output of said'second inverter a modulation waveform, and synchronizing means responsive to said control isignal including ya second diierentiator, means coupling, the output of said modulator gate generator to said second dilerentiator, and a phase splitterl coupled to the output of'said second ditferentiator whereby a synchronizing pulse is obtained as the output of said` phase splitter each time there is'an output of said rectied signal from said revolution per minute gate.

. 7. A modulator signal generator according to claim 6 wherein said bootstrap timing generator includes means tovary the repetition rate of said controlsignal.

8. A modulation signal generator comprising a source of `sine. wave signals, means to rectify said sine wave signals coupled to said source, means toygenerate a control signal `responsive .to` said sine wave signals including a squarer coupled to the output of. said source, a rst dilerentiator, means coupling said first diierentiator to said squarer, a first inverter, an' amplitude sensitive gate,

means coupling the .negative output of vsaid first differ- Y entiator to said rst inverter, means coupling the positive output of said dilerentiator to said amplitude sensitivev gate, a modulator gate generator, means coupling the outputs of said first inverter and said amplitude sensitive 'gate to said modulator gate generator, a boot strap timing generator, an electronic switch coupling the output of said modulator gate generator to said bootstrap tim-v `ing generator, means coupling the output of said boot strap timing generator to said amplitudesensitive gate;

a revolution perf'minute gate .coupled tothe output of said Vrectifying means, means coupling the output of said modulator gate generator to said revolution per minute gate to pass certain of said rectied'sine wave signals responsivev to the output of said modulator gate generator, a second inverter, means coupling the output of said revolution per minute gate to said second inverter to obtain `as the output of said second inverter a modulation waveform, synchronizing means responsive pulse Shaper, a second squarer coupling said pulse oscillator to said pulse Shaper, a pulse width multivibrator,

" means coupling the output of .said pulse Shaper to said pulse width multivibrator, athird inverter, a modulator,

means coupling the output of said third inverter to said modulator, switching means coupling the Y modulation waveform output of said second inverter to said modulator, a fourth inverter, means coupling the output of said modulator to said fourth inverter whereby an output is obtained from said inverter of a modulated pulse having the envelope of the modulation waveform output of said second inverter.

References Cited in the tile of this patent UNITED STATES PATENTS 2,510,299 Schramm June 6, 1950 2,555,442 Hales June 5, 1951 2,5%,587 Miller July 17, 1951 2,698,432 Blasingame Dec. 28, 1954 Bedford -s Jan. l, 1957 

